Systems, methods and devices for stabilizing one or more bone structures of a patient have been available for many years. Prior art procedures typically require large incisions and also significant tissue manipulation to adequately expose the areas intended for the attachment. The procedures are associated with long recovery times and increased potential for adverse events, such as infection, usually associated with muscle and other tissue trauma and scarring.
Currently available minimally invasive techniques and products are limited. These procedures are difficult to perform, especially in spinal applications in which the attachment points are deeper in tissue, and damage to neighboring tissue must be avoided. Many of the currently available less invasive products remain somewhat invasive due to component configurations and required manipulations to be performed during the attachment.
In reference specifically to treatment of the spine, FIGS. 1A-1B illustrate a portion of the human spine having a superior vertebra 2 and an inferior vertebra 4, with an intervertebral disc 6 located in between the two vertebral bodies. The superior vertebra 2 has superior facet joints 8a and 8b, inferior facet joints 10a and 10b, posterior arch 16 and spinous process 18. Pedicles 3a and 3b interconnect the respective superior facet joints 8a, 8b to the vertebral body 2. Extending laterally from superior facet joints 8a, 8b are transverse processes 7a and 7b, respectively. Extending between each inferior facet joints 10a and 10b and the spinous process 18 are lamina 5a and 5b, respectively. Similarly, inferior vertebra 4 has superior facet joints 12a and 12b, superior pedicles 9a and 9b, transverse processes 11a and 11b, inferior facet joints 14a and 14b, lamina 15a and 15b, posterior arch 20, spinous process 22.
The superior vertebra with its inferior facets, the inferior vertebra with its superior facets, the intervertebral disc, and seven spinal ligaments (not shown) extending between the superior and inferior vertebrae together comprise a spinal motion segment or functional spine unit. Each spinal motion segment enables motion along three orthogonal axis, both in rotation and in translation. The various spinal motions are illustrated in FIGS. 1C-1E. In particular, FIG. 1C illustrates flexion and extension motions, anterior translation, and axial loading, FIG. 1D illustrates lateral bending motion and lateral translation motion and FIG. 1E illustrates rotation. A normally functioning spinal motion segment provides physiological limits and stiffness in each rotational and translational direction to create a stable and strong column structure to support physiological loads.
Various disorders of the spine can produce debilitating pain that can affect a spinal motion segment's ability to properly function. The specific location or source of spinal pain is most often an affected intervertebral disc or facet joint. Often, a disorder in one location or spinal component can lead to eventual deterioration or disorder, and ultimately, pain in the other.
Spine fusion (arthrodesis) is a procedure in which two or more adjacent vertebral bodies are fused together. While spine fusion generally helps to eliminate certain types of pain, it has been shown to decrease function by limiting the range of motion for patients in flexion, extension, rotation and lateral bending. Furthermore, the fusion creates increased stresses on adjacent non-fused motion segments and accelerated degeneration of the motion segments.
Various technologies and approaches have been developed to treat spinal pain without fusion in order to maintain or recreate the natural biomechanics of the spine. To this end, significant efforts are being made in the use of implantable artificial intervertebral discs. Unfortunately, the currently available artificial discs do not adequately address all of the mechanics of motion for the spinal column.
It has been found that the facet joints can also be a significant source of spinal disorders and debilitating pain. Current interventions for the treatment of facet joint disorders have not been found to provide completely successful results.
Most recently, surgical-based technologies, referred to as “dynamic posterior stabilization,” have been developed to address spinal pain resulting from more than one disorder, when more than one structure of the spine have been compromised. An objective of such technologies is to provide the support of fusion-based implants while maximizing the natural biomechanics of the spine. Dynamic posterior stabilization systems typically fall into one of two general categories: (1) interspinous spacers and (2) posterior pedicle screw-based systems.
Examples of interspinous spacers are disclosed in U.S. Pat. Nos. Re. 36,211, 5,645,599, 6,695,842, 6,716,245 and 6,761,720.
Examples of pedicle screw-based systems are disclosed in U.S. Pat. Nos. 5,015,247, 5,484,437, 5,489,308, 5,609,636 and 5,658,337, 5,741,253, 6,080,155, 6,096,038, 6,264,656 and 6,270,498. These types of systems involve the use of screws which are positioned in the vertebral body through the pedicle. Certain types of these pedicle screw-based systems may be used to augment compromised facet joints, while others require removal of the spinous process and/or the facet joints for implantation. One such system, employs a cord which is extended between the pedicle screws and a fairly rigid spacer which is passed over the cord and positioned between the screws. While this system is able to provide load sharing and restoration of disc height, because it is so rigid, it is not effective in preserving the natural motion of the spinal segment into which it is implanted. Other pedicle screw-based systems employ joints between the pedicle screws that provide some discreet amounts of movement in different directions to somewhat simulate the complex movement of the spine.
There remains a need for minimally invasive methods and devices for bone stabilization procedures, including but not limited to dynamic spinal segment stabilization procedures and multi-level procedures for stabilizing more than two spinal segments. Furthermore, there is an ongoing need for systems that provide easier insertion for the clinician. Systems that allow simplified multiple degree of freedom of adjustment during implantation that then can be securely fixed are needed as are systems that can reduce fatigue failures, avoid large stresses between components under all load conditions and generally have a long implant life.